Flux guide for a magnetic fuze



Oct. 17, 1967 c. A. KESSLER FLUX GUIDE FOR A MAGNETIC FUZE 2 Sheets-Sheet 1 Filed Oct. 28, 1958 A V l /lldf/ll/l/ll/ INVENTOR. CLETUS A. KESSLER ATTORNEY Oct. 17, 1967 c. A. KESSLER FLUX GUIDE FOR A MAGNETIC FUZE 2 Sheets-Sheet 2 Filed 001;. 28, 1958 INVENTOR. CLETUS A, KES SLER BY I l jflfl/Z;

ATTORNEY.

United States Patent ()fifice 3,347,165 Patented Oct. 17, 1967 Navy Filed Oct. 28, 1958, Ser. No. 770,233 4 Claims. (Cl. 10270.2)

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a means for increasing the energy output of a magnetic fuze system and more particularly to ,a soft-iron flux guide assembly adapted to be mounted on a missile to provide a housing for the pickup coil and magnet assembly of a magnetic fuze system.

The sensing element of a magnetic fuze is basically a coil of wire in the near vicinity of a plurality of permanent magnets and the coil-magnet assembly in turn is mounted on or within the missile. When the missile approaches a conducting surface, such as a portion of an aircraft target, eddy currents are generated in the target skin. The changing field of the eddy currents due to the relative movement between the missile and target generates an EMF in the coil which can be used either to trigger a conventional thyratron firing circuit or to directly fire detonators of fairly low input energy requirements.

In magnetic fuze system of the type heretofore devised for guided missiles it has been the general practice to mount the pick-up or sensing coil concentrically with the axis of the missile either outside the missile skin or completely enclosed within the missile skin. When the coil is mounted outside the missile skin the non magnetic material (such as air) is used to couple the magnetic flux from the target to the pick-up coil and thus provide a high reluctance path for the changing field of the eddy current decreasing the possible energy output of the coil. Also eddy currents produced in the missile skin have been a serious problem both to coils mounted on the outside and on the inside of the missile skin because of the pronounced loss of energy due to the shielding effect caused by eddy currents circulating in the skin.

In the prior fuzes where the coil-magnet assemblies are placed within a missile enclosure, a reduced signal is obtained because of the shielding from the flow of eddy currents in the conducting enclosure. Since the eddy currents always flow in the missile enclosure in a direction such as to resist changes in the magnetic generating field, there would be no penetration of the field into space outside the enclosure if the magnets and coil are completely enclosed by a perfect conductor. Even if the enclosure has a finite conductivity, a reduced net field will still exist within the enclosure.

The present invention comprises primarily a soft iron flux guide mounted flush with the missile skin and having a recessed portion concentric with the missile enclosure with its face open outwardly, wherein the magnets and pick-up coil of the fuze system are mounted. The instant invention, therefore, overcomes both the deficiencies of the prior systems set forth above, because the soft iron flux guide makes a lower reluctance path for the magnetic field signal, and the magnetic fuze signal from the target is in a sense guided through the soft iron guide substantially by passing the aluminum missile skin which caused the serious loss of energy due to eddy currents in the skin.

It is an object of the present invention, therefore, to provide ,a new and improved magnetic fuze for a guided missile.

' and concentric with the Another object of the invention is to provide a means for mounting the magnets and sensing coil of a magnetic fuze on a missile whereby the shielding effect of the eddy currents produced in the missile skin is substantially eliminated.

Another object of the invention is to provide an improved magnetic fuze system wherein a low reluctance path for the target signal is provided from the target to the sensing coil.

A still further object of the invention is to provide a flux guide for a magnetic fuze sensing coil whereby the operating range of the fuze system is increased.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a partial cross-sectional view of a missile body incorporating one preferred embodiment of the present invention;

FIG. 2 is a partial cross sectional view of a missile body incorporating a second preferred embodiment of the invention;

FIG. 3 is a cross-sectional view of a third preferred embodiment of the instant invention;

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 3;

FIG. 5 is a cross-sectional view taken along line 55 of FIG. 3; and

FIG. 6 is an end view of the embodiment in FIG. 3.

Referring now to the drawings for a more complete understanding of the invention and more particularly to FIG. 1 thereof on which is shown a portion of a missile body 10 comprising a casing or missile skin enclosure 11 which is normally made of aluminum and has a rectangular recessed opening 12 formed around the body of the missile and concentric with the longitudinal axis thereof.

In the species of the invention illustrated in FIG. 1 a soft iron flux guide or sleeve member 13 normally made of grade A transformer iron, is formed as a cylinder with an outside diameter equal to the outside diameter of the missile enclosure 11. An off-set annular portion 14, formed in a channel-shape to fit within the recessed opening 12 of the missile body 11, is provided substantially in the center of the sleeve 13 with the remainder of the sleeve extending fore and aft of the missile body 11 flush with the skin of the missile. The sleeve 13 can be either a solid or laminated member however, the sleeve shown is laminated. A plurality of magnets 15 are mounted longitudinally in the recess 14 and spaced concentrically around the axis of the missile (only one is shown in FIG. 1). The magnets 15 are secured at one end to the vertical wall of the recess 14 by any suitable means (not shown) and the other end is secured by any suitable means (not shown) to a channel shaped circular member 16 made of any suitable insulating material and mounted within the recessed opening 14. A sensing or pick-up coil 17 is wound within the member 16 in such a manner as to be flush with the missile skin.

The second preferred embodiment of the invention illustrated in FIG. 2 comprises a rectangular recessed opening 22 similar to the opening 12 of the above described embodiment formed around the body 11 of the missile 10 longitudinal axis thereof. A soft iron fiux guide or circular sleeve member 23 is formed with a recessed annular portion 24 to line the opening 22 with the remainder of the sleeve 23 extending fore and aft of the opening 22 along the missile body 11 and flush with the missile skin.

A plurality of magnets 25 (only one is shown in FIG.

2) are mounted radially in the missile body 11 and project outwardly along the center line of the recess portion 24. A sensing or pick-up coil 27 is wound within the recessed portion 24 and surrounds the outer end portion f the magnets 25.

With reference to the third embodiment illustrated in FIGS. 3 through 6 the soft iron flux guide member 33 is actually a cylindrical section of the missile body being normally mounted between two aluminum sections (not shown) and is thus unlike the sleeves 13 and 23 of the two embodiments described above. A ring magnet 35 is mounted within a recessed channel shaped portion 32 of the guide member 33 by any suitable means (not shown) and a sensing coil 37 is wound around a circular angle insulating member 36.

The action of the prior magnetic fuzes can be compared to that of a rather poor transformer. Currents are generated in the target by the motion of the permanent magnets of the fuze relative to the target. The target, acting as a primary coil, then causes currents to be induced in the fuze coil in proportion to the flux linkage between target and coil. Since it is well known that a soft iron core increases the flux linkage between the primary and secondary coils of a transformer, the soft iron flux guide of the present invention, by analogy, increases the flux linkage between the target and the sensing or pick-up coil of the magnetic fuze circuit.

In the species of the instant invention, shown in FIGS. 1 and 2. the flux density of the magnetic field is concentrated near the outer surface of the soft iron cylinder that acts as a flux guide whereby only a relative small portion penetrates to the interior where it would produce eddy currents in the aluminum shell of the missile. In order to take advantage of this flux concentration, the fuze sensing coil is wound outside the soft iron cylinder and in a trough portion whereby the shielding effect of the eddy currents in the missile skin is virtually eliminated. Also eddy currents produced in the soft iron flux guide will be damped out rapidly because of the lower conductivity of the soft iron.

The magnets in the initial invention are also placed within the recessed trough portion in positions such that the iron flux guide will not close the static magnetic fiel path of the missile fuze and thereby decrease the density of the inducing field outside the fuze configuration.

The type of construction of the flux guide depends upon the type of missile it is to be used on and the missile limitations. It is to be noted, however, that when a sleeve type of flux guide is used (such as the sleeves in FIGS. 1 and 2) the sleeve should be as long as the mechanical specifications of the missile will allow, since a short iron sleeve in the immediate vicinity of the coil will result in only a slight inccrease of flux linkage.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the lit scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a missile, a magnetic fuze comprising in combination at least one permanent magnet, a sensing means adjacent said permanent magnet and operable to detect a magnetic flux signal from a target, means comprising a soft iron guide mounted on said missile and having a trough portion for mounting said permanent magnet and said serving means in said trough portion flush with the outer surface of the missile and operable to provide a lower reluctance path for said magnetic flux signal than provided by the missile whereby the output signal of said sensing means is increased and the shielding effect of eddy currents in the missile surface skin is substantially eliminated.

2. In a fuze system in a missile, at least one permanent magnet for setting up a magnetic field whereby eddy currents are generated in a target surface, a sensing means mounted adjacent to said permanent magnet and operable to sense the changing field of said eddy currents, and a flux guide means comprising a soft iron sleeve means having a recessed portion therein for housing said at least one permanent magnet and said sensing means mounted flush with the outer surface of the missile and providing a lower reluctance path for said eddy currents than the body of said missile, eddy currents being generated in the target surface when the missile approaches said target surface and said sensing means generating an output signal when influenced by said eddy current, whereby the flux guide means on said ensing the missile body is substanshielding effect of said means by eddy currents in tially eliminated.

3. The fuze system of claim 2 in which said sensing means comprises a pick-up coil wound around said flux guide means within said recessed portion.

4. The fuze system of claim 2 in which said flux guide means comprising a soft ir-on member is adapted to be mounted between two sections of a missile body and having an annular recessed portion therein for housing said magnet and sensing means whereby the shielding effect on said sensing means by eddy currents in the missile body is subtantially eliminated.

References Cited UNITED STATES PATENTS 7/1950 Allison l0270.2 8/1959 Statharn 10270.2

Examiners.

Assistant Examiners. 

1. IN A MISSILE, A MAGNETIC FUZE COMPRISING IN COMBINATION AT LEAST ONE PERMANENT MAGNET, A SENSING MEANS ADJACENT SAID PERMANENT MAGNET AND OPERABLE TO DETECT A MAGNETIC FLUX SIGNAL FROM A TARGET, MEANS COMPRISING A SOFT IRON GUIDE MOUNTED ON SAID MISSILE AND HAVING A TROUGH PORTION FOR MOUNTING SAID PERMANENT MAGNET AND SAID SERVING MEANS IN SAID TROUGH PORTION FLUSH WITH THE OUTER SURFACE OF THE MISSILE OPERABLE TO PROVIDE A LOWER RELUCTANCE PATH FOR SAID MAGNETIC FLUX SIGNAL THAN PROVIDED BY THE MISSILE WHEREBY THE OUTPUT SIGNAL OF SAID SENSING MEANS IS INCREASED AND THE SHIELDING EFFECT OF EDDY CURRENTS IN THE MISSILE SURFACE SKIN IS SUBSTANTIALLY ELIMINATED. 